if vSpeed is your rate. Rel movement can be converted to abs movement as fallows.
Code:
var vSpeed = 5;
VECTOR vec_move;
while()...
vec_set(vec_move,vector(key_w-key_s,key_a-key_d,0));
vec_rotate(vec_move,my.pan);
c_move(my,nullvector,vec_scale(vec_move,vSpeed*time_step),FLAGS);
...
// using abs movement your pan/tilt/roll can stay 0//
